Chemical-mechanical processing of a semiconductor wafer or substrate may include forming a dielectric layer over the semiconductor substrate, etching a plurality of trenches into the dielectric layer, and forming a metal layer, such as a tungsten layer, over the dielectric layer and the trenches, wherein the trenches are generally filled by the metal layer. A portion of the metal layer may be further removed via an abrasive polishing pad of a chemical-mechanical polishing (CMP) apparatus, wherein the polishing pad orbits with respect to the wafer. The wafer may further rotate with respect to the orbiting polishing pad, wherein a slurry composition is typically disposed on the side of the polishing pad in contact with the various layers on the wafer, and wherein the slurry composition assists in polishing and/or oxidizing the layers.
One problem conventionally seen in CMP processing involves metals remaining on product wafers after the CMP process is performed. A conventional CMP apparatus typically comprises circular polishing pads having grooves defined therein for slurry distribution to between the polishing pad and the wafer. In an orbiting CMP apparatus, excess metal can remain on a center of the wafer after the CMP process is complete due to a slow removal rate associated with a center of the conventional polishing pad.